JPH03179127A - Direct combustion chamber structure for direct injection type diesel engine - Google Patents

Abstract

PURPOSE:To accelerate a combustion speed and prevent any afterburning from occurring by forming a direct combustion chamber in a piston so as to be expanded in the radial direction toward the inmost recess from the central opening of a piston top face, while interconnecting the peripheral recess of the direct combustion chamber to a peripheral opening of the piston top face. CONSTITUTION:When a piston 16 goes up, volumetric capacity in a space at the more upper side than a piston top face 17 is decreased, and air at this upper side flows into a direct combustion chamber 22 by way of a center opening 24, a peripheral opening 28 and an interconnecting hole 30. At this time, this direct combustion chamber 22 is formed so as to have a large depth to the radial outside from the center opening 24, so that a large squish flow A is formed in the inner part. In addition, in and around a top dead center the piston 16, fuel is sprayed to a peripheral recess 26 of the direct combustion chamber 22 from a nozzle 20 as a spray. When the piston 16 further goes down, the volume in the more upper space than the piston top face 17 is increased, thus a flame in the direct combustion chamber 22 is jetted to the upper part of piston top face 17.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a direct combustion chamber structure of a direct injection diesel engine installed in a large automobile or the like.

More specifically, the present invention relates to a direct combustion chamber structure for a direct injection diesel engine that can increase the combustion rate.

[Conventional technology]

6 and 7 are cross-sectional views of a direct combustion chamber structure in a conventional direct injection diesel engine. 6 and 7, a heart-shaped direct combustion chamber 40 and a squish lip direct combustion chamber 42, respectively, are formed within the piston 16, opening into the top surface 17. In the direct combustion chamber 42 with a squish lip, the squish lip 44 is
It is formed along the periphery of the upper opening of the direct combustion chamber 42 with a squish lip so as to protrude slightly inward in the radial direction,
As the piston 16 reciprocates, the squish lip 44
As a result, a squish flow is generated in the direct combustion chamber 42 with a squish lip.

[Problem to be solved by the invention]

In recent years, measures against exhaust gas from diesel engines.

BACKGROUND ART Fuel ignition timing is delayed to piston top dead center or immediately thereafter to reduce the amount of NOx (nitrogen oxides) in exhaust gas discharged from a diesel engine.

When such a delay in the fuel ignition timing is performed in the heart-shaped direct combustion chamber 40 and the squishy ridged direct combustion chamber 42 as shown in FIGS. 6 and 7, the combustion end timing is also delayed, causing an afterburning phenomenon and reducing fuel efficiency. This leads to deterioration of fuel consumption, generation of black smoke, and increase in unburned components.

An object of the present invention is to quickly terminate combustion in a direct injection diesel engine despite the delay in fuel ignition timing, thereby solving the problems of the prior art described above.

[all! Means for Solving the Problem] In the direct combustion chamber structure of the direct injection diesel engine of the present invention, a central opening and a plurality of peripheral openings are formed at the center and peripheral portions of the top surface of the piston, respectively. The direct combustion chamber is formed inside the piston so as to expand radially from the central opening toward the back. Further, each peripheral opening directly communicates with the inner peripheral part of the combustion chamber via a communication hole.

[Operation] In the compression stroke, as the piston rises, the volume of the space above the top surface of the piston decreases, and the air above the top surface is directly combusted through the central opening, the peripheral opening and the communication hole. The direct combustion chamber that flows into the room is formed to have a sufficiently large depth from the center opening, so
A large squish flow is generated directly within the combustion chamber due to the air flowing directly into the combustion chamber from the central opening and the peripheral opening.

Fuel injection directly into the combustion chamber is sufficiently delayed to self-ignite. The flame quickly spreads directly into the combustion chamber in a squish flow.

During the explosion stroke, as the piston descends, the volume of the space above the top surface of the piston increases, and the flame in the combustion chamber directly flows above the top surface of the piston through the central opening, the communication hole and the peripheral opening. gush to. As a result, the air-fuel mixture above the top surface of the piston is quickly combusted.

〔Example〕

The present invention will be described below with reference to the embodiments shown in FIGS. 1 to 5.

1, 2, and 3 are diagrams showing the structure of the direct combustion chamber of the direct injection diesel engine 10 in the compression stroke, top dead center, and explosion stroke, respectively, and FIG. 4 is a diagram of the piston 16 viewed from above. It is. Direct injection diesel engine 1
0 is cylinder block 12 and cylinder block 12
A piston 16 reciprocates within the cylinder block 12. As the piston 16 reciprocates, the top surface 1
The volume of the space above 7 is increased or decreased, and a plurality of piston rings 18 are attached to one circumferential portion, and slide on the inner surface of the cylinder block 12 via the piston rings 18. The nozzle 20 is attached to the cylinder head 14 along the centerline of the piston 16, and injects fuel from a plurality of nozzle holes. The direct combustion chamber 22 has a top surface 17 at the central opening 24.
It opens at the center of the opening 24 and extends obliquely downward so as to spread outward in the radial direction from the central opening 24 toward the peripheral inner part 26, and has a circular cross section. A total of four peripheral openings 28 are formed in the same circumferential shape around the central opening 24 at 90° intervals in the circumferential direction in an arc shape on the top surface 17 . Each peripheral opening 28
communicates with the peripheral inner part 26 via a communication hole 30 parallel to the axis of the piston 16.

In FIG. 2, the jet 32 indicates a jet 1132 of fuel discharged from the nozzle 20, and in FIG.
4 and exhaust port 36 indicate the positions of intake boat 34 and exhaust port 36, respectively.

The operation of the embodiment will be explained.

In the compression stroke (FIG. 1), as the piston 16 rises, the volume of the space above the top surface 17 of the piston 16 decreases, and the air above the top surface 17 passes through the central opening 24 and the peripheral opening. 28 and the communication hole 30 directly into the combustion chamber 22
The direct combustion chamber 22 into which air flows in is formed to have a sufficiently large depth radially outward from the central opening 24, so that air can flow directly into the combustion chamber 22 from the central opening 24 and the peripheral opening 28. direct combustion chamber 22
A large squish flow (arrow A in FIG. 1) is generated inside the tank.

At the top dead center of the piston 16 (FIG. 2) and immediately after it, the nozzle 20 has its nozzle hole facing directly into the combustion chamber 22, and directs the fuel as a jet 32 toward the peripheral inner part 26 of the combustion chamber 22. gush to. The fuel spray 32 spontaneously ignites, and the flame quickly spreads directly into the combustion chamber 22 in a squish flow.

Explosion row 8! (FIG. 3), as the piston 16 descends, the volume of the space above the top surface 17 of the piston 16 increases, and the flame in the combustion chamber 22 directly passes through the central opening 24 and through the communication hole 30. Piston 16 via peripheral opening 28
It ejects above the top surface 17 (arrow B in Figure 3). As a result, the air-fuel mixture above the top surface 17 of the piston 16 is quickly combusted.

FIG. 5 is a graph showing the relationship between the crank angle and the pressure inside the cylinder. In the conventional technology (dashed line), as the fuel injection timing is delayed, afterburning occurs due to the slow combustion rate. On the other hand, in the example (actual battle), the combustion speed increases due to the generation of a large squish flow in the direct combustion chamber 22 and the ejection of flame from the central opening 24 and the peripheral opening 28, and combustion ends quickly.

〔Effect of the invention〕

In this invention, the direct combustion chamber is formed in the piston so as to expand in the radial direction from the center opening on the top surface of the piston toward the back, and the deep part of the n side of the direct combustion chamber is connected to the piston through the communication hole. It communicates with the peripheral opening on the top surface. Therefore, in the compression stroke, as the piston rises, a large squish flow is generated directly within the combustion chamber, and in the explosion stroke, as the piston descends, the flame moves above the top surface of the piston to the center opening and around the piston. The fuel is ejected from the opening, increasing the combustion speed of the fuel and preventing afterburning. Thereby, it is possible to improve fuel efficiency and suppress black smoke and unburned components while suppressing the amount of NOx in the exhaust gas.

[Brief explanation of drawings]

1 to 5 relate to embodiments of the present invention, and FIGS. 1, 2, and 3 show the direct combustion chamber structure of a direct injection diesel engine during the compression stroke, respectively. Figure 4 is a diagram showing the piston at top dead center and the explosion stroke. Figure 5 is a graph showing the relationship between crank angle and pressure in the cylinder. Figures 6 and 7 are graphs showing conventional FIG. 2 is a cross-sectional view of a direct combustion chamber structure in a direct injection diesel engine. 10... Direct injection diesel engine, 16...
Piston, 17...Top surface, 22...Direct combustion chamber, 2
4... Center opening, 26... Peripheral deep part, 28... Peripheral opening, 30... Communication hole. Figure 0 0 6 7 2 4 6 8 0 Direct injection day piston Top surface Direct combustion chamber Center opening Surroundings Rear area Surrounding opening Communication port Zell engine Figure 2 Figure Figure 0 Figure Figure □ Crank angle

Claims (1)

[Claims] (1) A central opening and a plurality of peripheral openings are formed at the center and peripheral parts of the top surface of the piston, respectively, so that the direct combustion chamber expands in the radial direction from the central opening toward the back. A direct combustion chamber structure for a direct injection diesel engine, characterized in that each peripheral opening is formed inside and communicates with the inner part of the periphery of the direct combustion chamber through a communication hole.